Mechanism Description of an Autolite PV3 Spark Plug

Johnson FCWR 304

Mechanism Description of an Autolite PV3 Spark Plug

Introduction. An Autolite PV3 spark plug is an automotive component used to ignite the fuel-air mixture in the cylinder of an internal combustion engine. The spark plug starts the combustion of gas by setting off a small spark at the appropriate time. This particular spark plug is most often used in motorcycles. The spark plug is cylindrical with an overall length of 2 1/2 inches, a maximum diameter of 3/4 inch, and a weight of two ounces. The three main parts of the spark plug are the main central conductor, the insulator, and the main body assembly.

Description of Parts. The central conductor is an electrical pathway for the positive current flow. It is one piece of metal 2 1/2 inches long and 3/16 inch in diameter, cylindrically shaped with a knob on one end. It is The central conductor runs down the center of the spark plug.

The insulator is an electrical nonconductor that prevents current flow from the central conductor to the engine block. It is a 2 1/4-inch porcelain sheath with a maximum diameter of 1/2 inch. The inside of the insulator is a hollow tube, 1/2 inch in diameter, through which the central conductor, which it is baked onto, except at the very top and bottom.

The main body assembly is a multipurpose structure that is used as an electrical pathway for negative current flow and for easy installation and anchoring of the spark plug. It has an irregular cylindrical shape with a hollow tube 1/2 inch in diameter running down its center, onto which the insulator is molded. The main body assembly is made of one piece of metal with a height of I inch and a maximum diameter of 3/4 inch. The main body assembly is divided into three subparts: the hexagon nut, the threads, and the electrode.

The hexagon nut provides a gripping surface for use in installation and removal of the spark plug. It is located at the uppermost section of the main body. It is a regular, six-sided polygon with a distance of 3/4 inch between the opposite flat sections of the polygon. The hexagon nut is constructed of the same metal as the main body and is continuous with it. The hexagon nut is usually gripped by a wrench when the spark plug is installed or removed.
The threads of the spark plug form a modified screw shaft to hold the spark plug in the cylinder head of the engine. They are located at the base of the main body and have a diameter of 1/2 inch and a height of 1/2 inch. The grooves of the threads are cut in a helix around the outside of the bottom section of the main body.
The electrode provides a pathway for the negative current flow. It is L-shaped, with a width of 1/8 inch and length of 1/4 inch. The electrode is located at the base of the threads and is constructed of the same metal as the rest of the main body. A small gap of about .025 to.030 inch is maintained between the electrode and the central conductor. When current is delivered, the electricity will jump this gap, causing a spark and igniting the fuel-air mixture.